Femoroacetabular impingement (FAI) has recently been suggested as a potential factor in the development of osteoarthritis of the hip. FAI can be defined as the abutment between the proximal femur and the acetabular rim and most typically affects young, active adults and presents clinically with groin pain. These structural abnormalities reduce the range of motion for these patients and repeated contact between the femoral neck and the acetabular cartilage and labrum can lead to degenerative changes in the hip joint cartilage. This cartilage can be either the articular cartilage covering the surface of the femoral head and the acetabulum or the labrum, which is a cartilaginous ring surrounding the rim of the acetabulum.
There are two distinct causes of FAI. The first type, known as “cam impingement”, is due to a nonspherical portion of the femoral head abutting against the acetabular rim, especially during flexion and internal rotation. This can result in abrasion of the acetabular cartilage which may result in avulsion from the labrum and subchondral bone. Damage to the acetabular cartilage generally occurs in the anterosuperior area of the acetabulum and can lead to separation of cartilage from the labrum. The second type of FAI is known as ‘pincer impingement’ and is more common in middle-aged athletic women. It results from the contact of the femoral head-neck junction and the acetabular rim. Repeated abutment leads to degeneration of the labrum, resulting in ossification of the acetabular rim and deepening of the acetabulum. The subchondral damage is located fairly circumferentially and usually only includes a narrow strip of acetabular cartilage. Generally, cam and pincer impingements do not occur in isolation and most cases involve a combination of both mechanisms and are classified as a mixed cam-pincer impingement.
Due to the recently elucidated ties between FAI and the development of early osteoarthritis, treatment of FAI has become more commonplace. FAI is often treated with surgery as it will not heal on its own. The surgical technique most often employed is an open surgical technique. For cam-type morphologies, the aim is to recreate a normal concave contour of the femoral neck by removing bone through a series of sequential osteotomies of small sleeves of bone from the femoral head-neck junction. For pincer-type morphologies, either a resection osteoplasty of the acetabular rim is performed or a reorientation of a retroverted acetabulum by a periacetabular osteotomy.
Current techniques for femoroacetabular impingement require exposing the joint such that the user can view the bones. Additionally, during the procedure, the amount of bone resection necessary is left to the user's judgment, which may prove to be difficult to manage. Removal of too much bone may result in an increased risk of fracture in the femoral neck or pelvis, while removal of too little bone may not resolve the impingement issue. In one method of removal, the bone is removed using a tool, such as a burr, that is controlled by the surgeon without any guidance thereby resulting in bone removal that is variable.
Thus, there exists a need for a more accurate and precise method for determining the correct amount of bone to remove and then precisely removing that amount of bone.